192 WARREN H. LEWIS AND MARGARET R. LEWIS 



The experiments on the regeneration of muscle in amphibia 

 also show that there is a return first to ah embryonic type of 

 muscle cell followed by a redifferentiation in a manner similar 

 to the differentiation of embryonic cells. These myoblasts 

 come from the injured muscle fibers (Fraisse, Barfurth and 

 Towle). According to Towle, the outer bundles of the cut 

 nmscle disintegrate leaving nuclei surrounded by cytoplasm. 

 The nuclei increase in number by amitosis. Some of the cells 

 thus formed later divide by mitosis and from them are formed new 

 muscle fibers. The inner bundles of the muscle do not disin- 

 tegrate but spht longitudinally into myoblasts which later dif- 

 ferentiate into muscle. Barfurth finds that in the very young 

 larvae of Siredon, terminal and lateral buds grow from the in- 

 jured fibers. The outgrowths contain nuclei and form sarco- 

 blasts (myoblasts) and these differentiate into muscle fibers in 

 the same way as do the myoblasts of the normal embryo. In 

 the older larvae of the frog and in mature animals, there occurs a 

 degeneration of the muscle with the accumulation of nuclei and 

 the formation of giant cells. He also finds that there is a split- 

 ting of old fibers into myoblasts as well as sarcoblast-like out- 

 growths which form myoblasts which later become new muscle 

 fibers. 



The initial stages in the process of regeneration of muscle 

 in mammals and amphibia are in many respects very much like 

 the behavior of muscle in our cultures. In both there is (1) a 

 formation of young myoblasts, a return to a more embryonic 

 condition; (2) the formation of protoplasmic buds which grow 

 out from the ends of the old fibers. Such buds contain many 

 nuclei and lack cross-striations. 



The factors involved in the formation of these muscle buds 

 are probably the same in the tissue cultures and in regeneration 

 and consequently are common to each. We can eliminate at 

 the outset then various possible factors that are present where 

 muscle buds are formed in the regeneration of muscle in the 

 experimental animals, such as the influence of the nervous sys- 

 tem, of substances brought by the blood or body fluids or of 

 other influences that might come from the organism itself. 



